Various conditions, such as degenerative diseases, may result in the herniation of a spinal disc. This can often result in debilitating symptoms, including intractable pain, weakness, sensory loss, and incontinence. If conservative treatment of this condition is not successful, a surgical procedure known as a discectomy may be performed wherein at least a portion of the herniated disc is removed. In some instances, another surgical procedure may be performed to fuse together the two vertebrae adjacent the affected disc space. This is accomplished by removing the cartilaginous base members of the adjacent vertebrae and inserting a bone graft or other endoprosthesis between the two vertebrae.
In an attempt to provide more flexibility at the affected disc space, various intervertebral endoprostheses have been developed that include a pair of base members and a center body, or core, which may be resilient or made of metal, disposed between the base members. When inserted into the affected intervertebral disc space, each base member is placed in contacting engagement with one of the adjacent vertebrae. Known intervertebral endoprostheses of this type may be subject to one or more of the following disadvantages, depending upon the particular configuration of the prostheses: inadequate compliancy and failure to replicate the non-linear force versus displacement and damping characteristics of a natural disc; failure to permit the full range-of-motion that is available with a natural disc or insufficient stability (unconstrained); and undesirable wear on surfaces that slide relative to one another.
In view of the foregoing, it may be appreciated that there is a need for improved intervertebral endoprostheses as an alternative to bone fusion grafts and other known intervertebral endoprostheses.